1. Field of the Invention
The present invention relates to an optical information recording medium such as an optical disc or an optical card, and to a recording/reproducing apparatus for such the recording medium.
2. Description of the Related Art
Generally, a disc area of a recordable optical disc is divided into a user recording area and a pit recording area recorded with various control information. The various control information is such information as an address information related to the user recording area, an information for a most suitable recording power and a recording waveform, a provenance information (such as a manufacturing information), or a copy administrative information, or a copy protection information etc.
The information of which to be recorded and the recording method for such information depend on a format of the user recording area. The user recording area contains a groove for tracking. There are provided format types of a groove format for a recording information only on the groove and a land-groove format for the recording information on both land and groove.
As focusing on a physical figuration of the groove, there are two differences in the groove format and land-groove format. First, the groove format has a physically narrower track pitch than the land-groove format. The track pitch for land-groove format in view of information is a width of the land or groove, and the physical track pitch for the land-groove format will be a sum of both widths. On the other hand, the groove format has a physical track pitch equivalent to the track pitch in view of information, and the groove width for the recording information is equivalent to a half width of the track pitch. Accordingly, the track pitch for groove format is equivalent to approximately a half width of the track pitch of land-groove format.
Second, the groove format has a shallower phase depth than the land-groove format. The land-groove format utilizes a groove having a phase depth of approximately λ/6 to suppress cross-talk from the land to groove or the groove to land at the reproducing condition. The “λ” represents a wavelength of reproducing light source. On the other hand, the groove format utilizes a shallower phase depth because it has a thinner groove width that the reproducing output of recorded information is low. Typically, the phase depth is less than λ/8. The phase depth depends on a disc system, for example, a magneto-optical disc utilizes a λ/8 phase depth. Further, disc types of a phase change optical disc, such as CD-RW and DVD-RW discs, utilize a phase depth of less than λ/10, desirably less than λ/15. The reason why the phase depth of groove is shallower in the latter is that to maintain compatibility with a ROM type disc in a signal to be used. Further, a system for a next generation such as the system using a semi-conductor laser of 400 nm wavelength utilizes shallower groove of less than λ/10, desirably λ/13 to λ/20 to obtain higher level of reproducing signal.
The following is the reason why that the groove format is superior to the land-groove format. The land-groove format has a problem of having a different amount of offset for a land or a groove at the optimum operating point in a focus or a tracking servo system under recording/reproducing operation. On the other hand, as to the groove format, the information is recorded on to a groove of single stroke line from inner to outer circumference so that the disc format can be simple and the recording/reproducing operation for the disc can be simple. Further, a disc of the ROM type also has a groove of single stroke line so that the compatibility of format between a ROM type disc and a recordable disc can be maintained.
The groove format does not have a problem of having a different offset amount in optimum operating point of the focus and tracking servo system. Accordingly, the groove format is considered to be advantageous for the next generation format. A recording/reproducing method for the groove format has been disclosed in the Japanese Patent Laid-open Publication No. 10-222874 that the information is recorded on or reproduced from an optical information recorded medium having an information area of a Lin (Lead-in) area where the PCA, PMA, an address information and a control information necessary for recording and reproducing superimposed on a wobbling pregroove as a preformat information, a program area where the user information constitutes a pregroove and a Lout (Lead-out) area, from an inner to outer circumferences, by being synchronized with preformat information and controlling revolution of the disc and a pulse for recording data. The pregroove is wobbled based on the standard signal having a predetermined frequency combined with an address information and a control information.
However, if the control information has been recorded wobblingly, it is difficult to wobble the groove in high speed and consequently, an amount of information which can be recorded decreases. To solve this problem, information is recorded by utilizing a pit format like the land-groove format.
The pit and groove should be formed in a same depth because the pit and groove is recorded on a photo-register applied to an original glass disc with an original disc recording apparatus. Based on the original disc recorded as mentioned above, a plastic disc will be manufactured. A plastic molding and transcription or the like for the pit and groove slightly differs from each other but the phase depth of the pit and groove will be technically the same. A disc manufactured as mentioned above having the same phase depth of the pit and groove with less than λ/10 nm can provide with only a very small amount of reproducing signals. Such a reproducing signal has a small level with less S/N ratio, which is not sufficient for decoding. In addition, making different phase depth for each pit and groove will cause a manufacturing process for optical information recording disc complicated and decrease a manufacturing productivity.